Method and system of operating a bi-directional double-base bipolar junction transistor (B-TRAN)

ABSTRACT

Operating a bi-directional double-base bipolar junction transistor (B-TRAN). One example is a method comprising: conducting a first load current from an upper terminal of the power module to an upper collector-emitter of the transistor, through the transistor, and from a lower collector-emitter to a lower terminal of the power module; and then responsive assertion of a first interrupt signal, interrupting the first load current from the lower collector-emitter to the lower terminal by opening a lower-main FET and thereby commutating a first shutoff current through a lower base of the transistor to the lower terminal; and blocking current from the upper terminal to the lower terminal by the transistor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional App. No.63/123,704 filed Dec. 10, 2020. The provisional application isincorporated by reference herein as if reproduced in full below.

BACKGROUND

A bi-directional double-base bipolar junction transistor (hereafterB-TRAN) is junction transistor constructed with a base andcollector-emitter on a first side of the bulk region, and a distinct andseparate base and collector-emitter on a second side of the bulk regionopposite the first side. When properly configured by an external driver,electrical current may selectively flow through a B-TRAN in eitherdirection, and thus B-TRAN devices are considered bi-directionaldevices. Based on the bi-directionality, whether a collector-emitter isconsidered a collector (e.g., current flow into the B-TRAN) or anemitter (e.g., current flow out of the B-TRAN) depends on the polarityof the applied external voltage and thus the direction of current flowthrough the B-TRAN. Consider, as an example, current flow through aB-TRAN device in a particular direction, such as from an uppercollector-emitter to a lower collector-emitter. In such a situation, theupper collector-emitter acts a collector, and the lowercollector-emitter acts as an emitter.

SUMMARY

At least one example is a method of operating a power module havingbi-directional double-base bipolar junction transistor, the methodcomprising: conducting a first load current from an upper terminal ofthe power module to an upper collector-emitter of the transistor,through the transistor, and from a lower collector-emitter to a lowerterminal of the power module; and then responsive assertion of a firstinterrupt signal interrupting the first load current from the lowercollector-emitter to the lower terminal by opening a lower-main FET andthereby commutating a first shutoff current through a lower base of thetransistor to the lower terminal; and blocking current from the upperterminal to the lower terminal by the transistor.

In the example method: interrupting the first load current may furthercomprise interrupting the first load current with the lower-main FEThaving a breakdown voltage of 100 Volts or less; and blocking currentmay further comprise blocking at an applied voltage across the upperterminal and the lower terminal of 600 Volts or greater.

The example method may further comprise, after blocking current from theupper terminal to the lower terminal: conducting a second load currentfrom the lower terminal of the power module to the lowercollector-emitter, through the transistor, and from the uppercollector-emitter to the upper terminal; and then responsive toassertion of a second interrupt signal interrupting the second loadcurrent from the upper collector-emitter to the upper terminal byopening an upper-main FET and thereby commutating a second shutoffcurrent through an upper base to the upper terminal; and blockingcurrent from the lower terminal to the upper terminal by the transistor.In the example method: interrupting the second load current may furthercomprise interrupting the second load current with the upper-main FEThaving a breakdown voltage of 100 Volts or less; and blocking currentfrom the lower terminal to the upper terminal may further compriseblocking at an applied voltage across the lower terminal and the upperterminal of 600 Volts or greater.

Another example is a switch assembly comprising: an upper terminal, alower terminal, and an upper-control input; a transistor defining anupper base, an upper collector-emitter, a lower base, and a lowercollector-emitter; an upper-main FET defining a first lead coupled tothe upper terminal, a second lead coupled to the uppercollector-emitter, and a gate; a lower-main FET defining a first leadcoupled to the lower collector-emitter, a second lead coupled to thelower terminal, and a gate; and a controller coupled to theupper-control input, the gate of the upper-main FET and the gate of thelower-main FET, and for a first applied voltage across the upperterminal and lower terminal. The controller may be configured to: assertthe gate of the upper-main FET to make the upper-main FET conductive,arrange the transistor for conduction from the upper collector-emitterto the lower collector-emitter, and assert the gate of the lower-mainFET to make the lower-main FET conductive such that a first load currentflows from the upper terminal to the lower terminal; sense de-assertionof the upper-control input; and responsive to de-assertion of theupper-control input de-assert the gate of the lower-main FET tointerrupt the first load current and thereby commutate a first shutoffcurrent through the lower base to the lower terminal; and arrange thetransistor to block current flow from the upper terminal to the lowerterminal.

In the example switch assembly, the breakdown voltage of the transistormay be is 600 Volts or greater, and the breakdown voltage of thelower-main FET may be 100 Volts or less.

In the example switch assembly, the breakdown voltage of the transistormay be about 1200 Volts, and the breakdown voltage of the lower-main FETmay be 80 Volts or less.

The example switch assembly may further comprise an upper-base FEThaving a first lead coupled to the upper base, a second lead coupled tothe upper terminal, and a gate, and during periods when the first loadcurrent flows from the upper terminal to the lower terminal, theupper-base FET is conductive. And when the controller arranges thetransistor to block current flow from the upper terminal to the lowerterminal, the controller may be further configured to de-assert the gateof the upper-base FET to electrically float the upper base.

The example switch assembly may further comprise a lower-control inputcoupled to the controller. And for a second applied voltage across theupper terminal and lower terminal, the second applied voltage having apolarity opposite the first applied voltage, the controller may befurther configured to: assert the gate of the lower-main FET to make thelower-main FET conductive, arrange the transistor for conduction fromthe lower collector-emitter to the upper collector-emitter, and assertthe gate of the upper-main FET to make the upper-main FET conductivesuch that a second load current flows from the lower terminal to theupper terminal; sense de-assertion of the lower-control input; andresponsive to de-assertion of the lower-control input de-assert the gateof the upper-main FET to interrupt the second load current and therebycommutate a second shutoff current through the upper base to the upperterminal; and arrange the transistor to block current flow from thelower terminal to the upper terminal. The example switch assembly mayfurther comprise a lower-base FET having a first lead coupled to thelower base, a second lead coupled to the lower terminal, and a gate, andduring periods when the second load current flows from the upperterminal to the lower terminal, the lower-base FET is conductive. Andwhen the controller arranges the transistor to block current flow fromthe lower collector-emitter to the upper collector-emitter, thecontroller may be further configured to de-assert the gate of thelower-base FET to electrically float the lower base. The breakdownvoltage of the transistor may be 600 Volts or greater, and the breakdownvoltage of the lower-main FET may be 100 Volts or less.

Another example is a method of operating a bi-directional double-basebipolar junction transistor, the method comprising: making thetransistor conductive from an upper collector-emitter to a lowercollector-emitter by supplying current to an upper base of thetransistor and electrically floating a lower base of the transistor; andthen making the transistor non-conductive by electrically floating theupper base, electrically floating the lower collector-emitter, andconducting a shutoff current through the lower base of the transistor.

In the example method, electrically floating the lower collector-emittermay further comprise making non-conductive a lower-mainelectrically-controlled switch having a first lead coupled to the lowercollector-emitter.

In the example method, making the transistor conductive may furthercomprise: closing an upper-main electrically-controlled switch coupledbetween an upper terminal and the upper collector-emitter; and closing alower-main electrically-controlled switch coupled between a lowerconductor terminal and the lower collector-emitter. Making thetransistor non-conductive may further comprise: opening the upper-mainelectrically-controlled switch; conducting the shutoff current to theupper collector-emitter through a diode associated with the upper-mainelectrically-controlled switch; and commutating the shutoff current fromthe lower collector-emitter to the lower base by opening the lower-mainelectrically-controlled switch.

In the example method, conducting the shutoff current through the lowerbase may further comprise conducting current through a diode associatedwith an electrically-controlled switch having a first lead coupled tothe lower base.

In the example method, supplying current to the upper base may furthercomprise at least one selected from a group comprising: supplyingcurrent at a base voltage about the same as a collector voltage appliedto the upper collector-emitter; and supplying current to the upper baseat the base voltage higher than the collector voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of example embodiments, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a cross-sectional elevation view of a B-TRAN in accordancewith at least some embodiments;

FIG. 2 shows an electrical schematic of an example switch assemblycomprising a model of a B-TRAN along with conceptual driver circuits, inaccordance with at least some embodiments;

FIG. 3 shows the example switch assembly in which the B-TRAN isnon-conductive, in accordance with example embodiments;

FIG. 4 shows the example switch assembly arranged for diode conduction,in accordance with at least some embodiments;

FIG. 5 shows the example switch assembly arranged for conduction, inaccordance with at least some embodiments;

FIG. 6 shows a related switch assembly arranged for transistor turn-off;

FIG. 7 shows the example switch assembly arranged for pre-turn off, inaccordance with at least some embodiments;

FIG. 8 shows a partial block diagram, partial electrical schematic, of aswitch assembly in accordance with at least some embodiments;

FIG. 9 shows a partial electrical schematic of a switch assembly inaccordance with at least some embodiments;

FIG. 10 shows a method in accordance with at least some embodiments; and

FIG. 11 shows a plot of transient times for transitioning to anon-conductive state in accordance with at least some embodiments.

DEFINITIONS

Various terms are used to refer to particular system components.Different companies may refer to a component by different names—thisdocument does not intend to distinguish between components that differin name but not function. In the following discussion and in the claims,the terms “including” and “comprising” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to . . . .” Also, the term “couple” or “couples” is intended tomean either an indirect or direct connection. Thus, if a first devicecouples to a second device, that connection may be through a directconnection or through an indirect connection via other devices andconnections.

“About” in reference to a recited parameter shall mean the recitedparameter plus or minus ten percent (+/−10%) of the recited parameter.

“Assert” shall mean changing the state of a Boolean signal. Booleansignals may be asserted high or with a higher voltage, and Booleansignals may be asserted low or with a lower voltage, at the discretionof the circuit designer. Similarly, “de-assert” shall mean changing thestate of the Boolean signal to a voltage level opposite the assertedstate.

“Bi-directional double-base bipolar junction transistor” shall mean ajunction transistor having a base and a collector-emitter on a firstface or first side of a bulk region, and having a base and acollector-emitter on a second face or second side of the bulk region.The base and the collector-emitter on the first side are distinct fromthe base and the collector-emitter on the second side.

“FET” shall mean a field effect transistor, such as a junction-gate FET(JFET) or metal-oxide-silicon FET (MOSFET).

“Closing” in reference to an electrically-controlled switch (e.g., aFET) shall mean making the electrically-controlled switch conductive.For example, closing a FET used as an electrically-controlled switch maymean driving the FET to the fully conductive state.

“Opening” in reference to an electrically-controlled switch (e.g., aFET) shall mean making the electrically-controlled switchnon-conductive.

“Upper base” shall mean a base of a bi-directional double-base bipolarjunction transistor on a first side of a bulk region of the transistor,and shall not be read to imply a location of the base with respect togravity.

“Lower base” shall mean a base of a bi-directional double-base bipolarjunction transistor on a second side of a bulk region of the transistoropposite a first side, and shall not be read to imply a location of thebase with respect to gravity.

“Upper collector-emitter” shall mean a collector-emitter of abi-directional double-base bipolar junction transistor on a first sideof a bulk region of the transistor, and shall not be read to imply alocation of the base with respect to gravity.

“Lower collector-emitter” shall mean a collector-emitter of abi-directional double-base bipolar junction transistor on a second sideof a bulk region of the transistor opposite a first side, and shall notbe read to imply a location of the base with respect to gravity.

“Injecting charge carries into [a base]” or “injection of chargecarriers into [a base]” (e.g., upper base, lower base) of a transistorshall not include directly coupling (e.g., through a transistor) thebase to a collector-emitter on the same side of the transistor.

“Extracting charge carries from [a base]” or “extraction of chargecarriers from [a base]” (e.g., upper base, lower base) of a transistorshall not include directly coupling (e.g., through a transistor) thebase to a collector-emitter on the same side of the transistor.

The terms “input” and “output” when used as nouns refer to connections(e.g., electrical, software), and shall not be read as verbs requiringaction. For example, a timer circuit may define a clock output. Theexample timer circuit may create or drive a clock signal on the clockoutput. In systems implemented directly in hardware (e.g., on asemiconductor substrate), these “inputs” and “outputs” define electricalconnections. In systems implemented in software, these “inputs” and“outputs” define parameters read by or written by, respectively, theinstructions implementing the function.

“Controller” shall mean, alone or in combination, individual circuitcomponents, an application specific integrated circuit (ASIC), amicrocontroller with controlling software, a reduced-instruction-setcomputing (RISC), a digital signal processor (DSP), a processor withcontrolling software, a programmable logic device (PLD), or a fieldprogrammable gate array (FPGA), configured to read inputs and driveoutputs responsive to the inputs.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

Various examples are directed to methods and systems of operating abi-directional double-base bipolar junction transistor (B-TRAN). Inparticular, various examples are directed to operating a B-TRAN in sucha way that the reductions in breakdown voltage between the uppercollector-emitter and the lower collector-emitter (and vice versa)caused by the Beta effect are reduced or eliminated, and shutoff time isreduced compared to three-terminal transistor turnoff. Moreparticularly, during a transistor-on mode the B-TRAN conducts loadcurrent, for example, from an upper collector-emitter to a lowercollector-emitter, and responsive to a control signal changing state theload current is initially interrupted by a lower-main FET having abreakdown voltage lower than the blocking voltage of the B-TRAN.Interrupting the load current commutates a portion of the load current(the commutated portion termed a shutoff current) through the B-TRAN tothe lower base. The shutoff current reverse biases a PN junction betweenthe upper collector-emitter and the lower base, which thus quicklyblocks current flow through the B-TRAN. Thereafter, the applied voltageis blocked by the B-TRAN. Load currents in the opposite direction (e.g.,from the lower collector-emitter to the upper collector-emitter) causedby an applied voltage of opposite polarity may be similarly initiallyinterrupted by an upper-main FET, and then blocked by the B-TRAN. Thespecification first turns to an example B-TRAN to orient the reader.

FIG. 1 shows a cross-sectional elevation view of an example B-TRAN. Inparticular, FIG. 1 shows a B-TRAN 100 having an upper face or upper side102 and a lower face or lower side 104. The designations “upper” and“lower” are arbitrary and used merely for convenience of the discussion.The upper side 102 faces a direction opposite the lower side 104. Stateddifferently, an outward pointing vector normal to the upper side 102(the vector not specifically shown) points an opposite direction withrespect to an outward pointing vector normal to the lower side 104 (thevector not specifically shown).

The upper side 102 includes collector-emitter contact regions 106 whichform a junction with the drift region or bulk substrate 108. The upperside 102 further defines base contact regions 110 disposed between thecollector-emitter contact regions 106. The collector-emitter contactregions 106 are coupled together to form an upper collector-emitter 112.The base contact regions 110 are coupled together to form an upper base114. Similarly, the lower side 104 includes collector-emitter contactregions 116 which form a junction with the bulk substrate 108. The lowerside 104 further defines base contact regions 118 disposed between thelower collector-emitter contact regions 116. The collector-emittercontact regions 116 are coupled together to form a lowercollector-emitter 120. The lower base contact regions 118 are coupledtogether to form a lower base 122.

The example B-TRAN 100 is an NPN structure, so the collector-emittercontact regions 106 and 116 are N-type, and the base contact regions 110and 118 are P-type. In the example system, a shallow N+ region providesohmic contact from collector-emitter contact regions 106 and 116 to therespective collector-emitters 112 and 120. Further in the examplesystem, shallow P+ contact doping provides ohmic contact from basecontact regions 110 and 118 to the respective bases 114 and 122. In thisexample, optional dielectric-filled trenches 124 provide lateralseparation between base contact regions and collector-emitter contactregions. Note that PNP-type B-TRAN devices are also contemplated;however, so as not to unduly lengthen the discussion a PNP-type B-TRANdevice is not specifically shown.

In example cases, the various structures and doping associated with theupper side 102 are meant to be mirror images of the various structuresand doping associated with the lower side 104. However, in some casesthe various structures and doping associated with the upper side 102 areconstructed at different times than the various structures and doping onthe lower side 104, and thus there may be slight differences in thestructures and doping as between the two sides, the differencesattributable to manufacturing tolerances, but such does not adverselyaffect the operation of the device as a bi-directional double-basebipolar junction transistor. In order to describe operation of theexample B-TRAN device, the specification now turns to a model of theB-TRAN device, along with a simplified driver circuits.

FIG. 2 shows an electrical schematic of an example switch assemblycomprising a model of a B-TRAN, along with a simplified electricalschematic of conceptual driver circuits. In particular, FIG. 2 shows amodel 200 of a B-TRAN, along with a driver portion 202 for the upperside of the B-TRAN and a driver portion 204 for the lower side of theB-TRAN. Turning first to the model 200, the example model 200 definesthe upper collector-emitter 112 and the upper base 114 (though in FIG. 2the upper base 114 is shown on the left side). The driver portion 202 iscoupled to the upper collector-emitter 112 and upper base 114. Theexample model 200 further defines the lower collector-emitter 120 andthe lower base 122 (though in FIG. 2 the lower base 122 is shown on theright side). The driver portion 204 is coupled to the lowercollector-emitter 120 and lower base 122.

Internally, the example model 200 comprises a first NPN transistor 206having an emitter E1 coupled to the upper collector-emitter 112, acollector C1 coupled to the lower collector-emitter 120, and a base B1defining the upper base 114. The example model 200 further includes asecond NPN transistor 208 having an emitter E2 coupled to the lowercollector-emitter 120, a collector C2 coupled to the uppercollector-emitter 112, and a base B2 defining the lower base 122. Thebases B1 and B2 are coupled together by series resistors 210 and 212representing the drift region of the bulk substrate, and the seriesresistors 210 and 212 defining a node 214 between them. A diode 216 iscoupled between the node 214 and the upper collector-emitter 112, andthe diode 216 represents the PN junction between the uppercollector-emitter 112 and the lower base 122. Similarly, a diode 218 iscoupled between the node 214 and the lower collector-emitter 120, andthe diode 218 represents the PN junction between the lowercollector-emitter 120 and the upper base 114.

External to the model 200, and referring initially to the upper driverportion 202, an electrically-controlled switch 222 (hereafter theupper-main switch 222) has a first lead coupled to the uppercollector-emitter 112 and a second lead coupled to and defining an upperterminal 224. The example upper-main switch 222 is shown as asingle-pole, single-throw switch in the open or non-conductiveconfiguration, but in practice the upper-main switch 222 may be a FET.Thus, when the upper-main switch 222 is conductive, the uppercollector-emitter 112 is coupled to the upper terminal 224. Anotherelectrically-controlled switch 226 (hereafter just switch 226) has afirst lead coupled to the upper terminal 224 and a second lead coupledto the upper base 114. The example switch 226 is shown as a single-pole,single-throw switch in the open or non-conductive configuration, but inpractice the switch 226 may be a FET. Thus, when the switch 226 isconductive, the upper base 114 is coupled to the upper terminal 224. Theexample driver portion 202 further comprises a source of charge carriers228 illustratively shown as a battery. The source of charge carriers 228has a negative lead coupled to the upper terminal 224. Anotherelectrically-controlled switch 230 (hereafter just switch 230) has afirst lead coupled to the positive terminal of the source of chargecarriers 228, and a second lead coupled to the upper base 114. Theexample switch 230 is shown as a single-pole, single-throw switch, butin practice the switch 230 may be a FET. Thus, when the switch 230 isconductive, the source of charge carriers 228 is coupled between theupper terminal 224 and the upper base 114.

Now referring to the lower driver portion 204, anelectrically-controlled switch 232 (hereafter the lower-main switch 232)has a first lead coupled to the lower collector-emitter 120 and a secondlead coupled to and defining a lower terminal 234. The examplelower-main switch 232 is shown as a single-pole, single-throw switch inthe open or non-conductive configuration, but in practice the lower-mainswitch 232 may be a FET. Thus, when the lower-main switch 232 isconductive, the lower collector-emitter 120 is coupled to the lowerterminal 234. Another electrically-controlled switch 236 (hereafter justswitch 236) has a first lead coupled to the lower terminal 234 and asecond lead coupled to the lower base 122. The example switch 236 isshown as a single-pole, single-throw switch in the open ornon-conductive configuration, but in practice the switch 236 may be aFET. Thus, when the switch 236 is conductive, the lower base 122 iscoupled to the lower terminal 234. The example driver portion 204further comprises a source of charge carriers 238 illustratively shownas a battery. The source of charge carriers 238 has a negative leadcoupled to the lower terminal 234. Another electrically-controlledswitch 240 (hereafter just switch 240) has a first lead coupled to thepositive terminal of the source of charge carriers 238, and a secondlead coupled to the lower base 122. The example switch 240 is shown as asingle-pole, single-throw switch, but in practice the switch 240 may bea FET. Thus, when the switch 240 is conductive, the source of chargecarriers 238 is coupled between the lower terminal 234 and the lowerbase 122.

FIG. 3 shows the example switch assembly in a mode in which the B-TRANis non-conductive and blocking current flow. The switches that arenon-conductive are shown as open circuits, and the switches that areconductive are shown as electrical shorts. In particular, consider anexternal applied voltage across the upper terminal 224 and lowerterminal 234 with the positive polarity on the upper terminal 224. Inthe configuration shown in FIG. 3 , the upper-main switch 222 isconductive along with the switch 236 in the lower driver portion 204,and all the remaining switches are non-conductive. With the upper-mainswitch 222 conductive, the upper terminal 224 is coupled to the uppercollector-emitter 112. With the switch 236 conductive, the lower base122 is coupled to the lower terminal 234. In the configuration shown,the PN junction shown as diode 216 of the model 200 is reversed biased.Moreover, both the lower collector-emitter 120 and the upper base 114are electrically floated. Thus, the B-TRAN is non-conductive for thepolarity of the applied voltage, there is no current flow through theB-TRAN, and thus B-TRAN is blocking the applied voltage (e.g., 1200Vfrom the upper terminal 224 to the lower terminal 234) by way of the PNjunction formed between the upper collector-emitter 112 and the lowerbase 122. The arrangement of FIG. 3 may therefore be referred to as thenon-conductive mode or the off mode.

Now consider that the B-TRAN is to be made conductive. FIG. 4 shows theexample switch assembly arranged for an optional diode-on mode. Inparticular, from the off mode of FIG. 3 , in order to initially make theB-TRAN conductive with the external applied voltage in the polarity asshown, the lower-main switch 232 is made conductive, switch 226 is madeconductive, and switch 236 is made non-conductive. The upper-main switch222 may be conductive or non-conductive in the diode-on mode. In theconfiguration shown, the upper PN junction illustrated by diode 216 isbypassed, and the lower PN junction illustrated by diode 218 is forwardbiased. Thus, current flows from the upper terminal 224, through upperbase 114 to the lower collector-emitter 120. When used, the diode-onmode may last predetermined period of time (e.g., about 1 microseconds(μs) to 5 μs, inclusive). In the configuration shown, the forwardvoltage drop is relatively low. In one example, the forward voltage dropis about 1.0V at a current density of about 200 A/cm2. However, theforward voltage drop can be lower.

FIG. 5 shows the example switch assembly arranged for conduction. Incases where the diode-on mode is used, in order to further lower theforward voltage drop across the B-TRAN, switch 226 is madenon-conductive, and switch 230 is made conductive. In cases where thediode-on mode is omitted, from the off mode (FIG. 3 ) the switch 236 ismade non-conductive, the lower-main switch 232 is made conductive, theswitch 230 is made conductive, and the upper-main switch 222 remainsconductive. In the configuration shown, the source of charge carriers228 is coupled between the upper terminal 224 and the upper base 114.The result is that the voltage on the upper base 114 is driven higherthan the voltage on the upper collector-emitter 112. Though the lowerbase 122 is electrically floated, the lower base 122 is internallyconnected through the drift region of the B-TRAN, and thus the lowerbase 122 may be (depending on the example voltage of the source ofcharge carriers 228) driven higher than the voltage on the uppercollector-emitter 112. Thus, both of the example transistors of themodel 200 are partially or fully conductive, and the arrangement istermed the conductive mode or the transistor-on mode. In theconfiguration, charge carriers (here holes) are injected into the upperbase 114 by way of the source of charge carriers 228. The additionalholes in the drift region increase the conductivity of the drift regionwhich lowers the forward voltage drop across the B-TRAN device. In oneexample, with an applied voltage of about 0.7V to about 1.0V, inclusive,across the upper collector-emitter 112 and upper base 114 (e.g., by thesource of charge carriers 228) the forward voltage drop may be reducedto between about 0.1V and 0.2V, inclusive. The discussion now turns torelated-art methods of making B-TRAN non-conductive, and potentialshortcomings of the related-art methods.

FIG. 6 shows a related-art switch assembly arranged for transistorturn-off. In particular, FIG. 6 shows the model 200 as discussed above,as well as two external switches 600 and 602. In related-art systems,switch 600 selectively couples the upper base 114 directly to the uppercollector-emitter 112, where the upper collector-emitter 112 defines theupper terminal. The switch 602 selectively couples the lower base 122directly to the lower collector-emitter 120, where the lowercollector-emitter 120 defines the lower terminal. Thus, for the exampleapplied voltage with the polarity shown, transistor turn-off is achievedby floating the upper base 114, and directly coupling the lower base 122to the lower collector-emitter 120. Making the B-TRAN non-conductive isthus achieved by draining charge carriers through the lower base 122 andthe lower collector-emitter 120 until the upper PN junction shown asdiode 216 becomes reversed biased. Making the B-TRAN non-conductive inthis way may be referred to as transistor turn-off.

Transitioning the B-TRAN to transistor turn-off by way of theconfiguration shown is a process that may have long “tail” as thecurrent asymptotically approaches zero, and thus takes an amount of timethat is not insubstantial. That is, the amount of time to reach zerocurrent flow through the B-TRAN using the related-art techniques maydepend on the amount of load current flowing through the B-TRAN, themagnitude of the applied voltage, and how quickly charge carriers aredrained from the drift region by way of the lower base 122. For example,based on simulations, transitioning from fully conductive carrying 100Aof current to non-conductive may take about 6 μs using the configurationshown in FIG. 6 . Various techniques may be implemented in therelated-art to reduce the transition time, such as a using anarrangement in which the switches 600 and 602 are both conductive for aperiod of time, but while such techniques may shorten the transitiontime, the current “tail” is still be present in the transition.

Moreover, implementing transistor turn-off as shown by FIG. 6 in therelated-art may reduce breakdown voltage. In particular, while theexample switch 602 is shown as conductive and thus directly coupling thelower base 122 to the lower collector-emitter, in practice the switch602 may be a transistor, such as a FET. Even a well designed andconstructed FET will have a non-zero voltage drop (e.g., between 0.1Vand 0.3V) in the fully conductive state. Additionally, the electricalconnections between the B-TRAN and the external driver circuit,including switch 602, each have a small but non-zero resistance. Theresult is that rather than the example lower base 122 and lowercollector-emitter 120 having the same potential, the lower base 122 maycarry a higher potential than the lower collector-emitter 120. Thehigher potential on the lower base 122, in combination with the Beta ofthe B-TRAN, increases leakage current and lowers the breakdown voltageof the B-TRAN from the upper collector-emitter 112 to the lowercollector-emitter 120. The lower breakdown voltage may be loweredfurther still as the temperature of the B-TRAN increases.

Further still, in many cases the example load current carried from theupper collector-emitter 112 to the lower collector-emitter 120 may beinductive in nature, either because the load itself is inductive (e.g.,a motor), the inductive effects of various connections associated withthe B-TRAN, or both. Related-art switch assemblies such as shown in FIG.6 may have difficulty transitioning to non-conductive in the presence ofinductive loads. Stated otherwise, the non-zero potential differencebetween the lower base 122 and the lower collector-emitter 120, incombination with an external inductive load, may render the B-TRAN veryslow to transition to non-conductive, and in some cases for higherinductive currents may render the B-TRAN unable to transition tonon-conductive.

The issues noted above are addressed, at least in part, in the exampleswitch assemblies by the use the upper-main and lower-main switches.Returning briefly to FIG. 5 , again FIG. 5 shows the example switchassembly arranged for transistor-on mode. That is, for the examplepolarity of the applied voltage, the load current is conducted from theupper terminal 224, through the upper-main switch 222 to the uppercollector-emitter 112, through the B-TRAN, and from the lowercollector-emitter 120 to the lower terminal 234 through the lower-mainswitch 232. In example systems, based on change of state of an interruptsignal or control signal (discussed more below), making the B-TRANnon-conductive involves interrupting the current flow by one of theupper-main or lower-main switches. With the example polarity of theapplied voltage of FIG. 5 , current is interrupted by the lower-mainswitch 232.

Returning to FIG. 3 . In accordance with some examples, transitioningthe switch assembly from conductive or transistor-on mode (shown in FIG.5 ) to non-conductive or off mode of FIG. 3 may involve againimplementing the arrangement of FIG. 3 . That is, in some examplestransitioning from the transistor-on mode (shown in FIG. 5 ) to the offmode may involve directly re-implementing the arrangement of FIG. 3 . Inparticular, making the switch assembly non-conductive may comprisemaking the switch 230 non-conductive, making the lower-main switch 232non-conductive, making switch 236 conductive, and leaving upper-mainswitch 222 conductive. Making the switch 230 non-conductive ceasesinjection of charge carriers through the upper base 114. Opening ormaking the lower-main switch 232 non-conductive interrupts the loadcurrent from the lower collector-emitter 120 to the lower terminal 234.Moreover, making the lower-main switch 232 non-conductive commutates aportion of the load current to flow through lower base 122 and theswitch 236. The commutated portion of the load current (i.e., theshutoff current) flows for a short period of time until the PN junctionillustrated as diode 216 between the upper collector-emitter 112 and thelower base 122 becomes reversed biased, and then the current drops tosubstantially zero. Once the PN junction shown as diode 216 is reversedbiased, the example system blocks current from the upper terminal 224 tothe lower terminal 234 by way of the B-TRAN. Making the B-TRANnon-conductive in this way may be referred to as a diode turn-off, whichis significantly faster than transistor turn-off. In other cases,transitioning the switch assembly from conductive to non-conductive maytake place by use of an optional pre-turn-off mode.

Using diode turn-off may have several advantages, though not alladvantages are necessarily present in all cases. In particular, inaddition to being faster than transistor turn-off, breakdown voltage ofdiode turn-off is higher than transistor turn-off. Furthermore, astemperature increases, breakdown voltage of a diode is increased.Moreover, under inductive loads, diode turn-off can block higher voltageand current during turn off than transistor turn-off.

FIG. 7 shows the example switch assembly arranged for an optionalpre-turn-off mode. In some examples, the initial process of making theB-TRAN non-conductive (e.g., about 0.1 μs to 5 μs before full turn-offfor a 1200V device) may involve making the switches 226 and 236conductive, making switch 230 non-conductive, and leaving the upper-mainswitch 222 and lower-main switch 232 conductive. Making switch 230non-conductive and making switch 226 conductive stops the injection ofcharge carriers from the source of charge carriers 228. Moreover, makingswitch 236 conductive causes a current drain or flow out of the driftregion. It follows these actions reduce and/or remove charge carriersfrom the drift region, take the B-TRAN out of saturation, and increaseforward voltage drop. The configuration is referred as the pre-turn-offmode. In one example, in the pre-turn-off mode the forward voltage dropfrom the upper collector-emitter 112 to the lower collector-emitter 120may rise to between about 0.9V and 3V, inclusive. The example B-TRAN maythen be made fully non-conductive, for the example polarity, byre-implementing the off mode of FIG. 3 . Implementing the pre-turn-offmode further decrease the amount of time to transition the switchassembly to the off mode (e.g., compared to changing the arrangement ofFIG. 5 to the arrangement of FIG. 3 directly).

The examples with respect to FIGS. 3-5 and 7 are for the situation ofthe external applied voltage having a positive polarity at the upperterminal 224. However, the example B-TRAN is a symmetrical device, andnow understanding how to control current flow through the B-TRAN in withexample polarity shown, control of current flow in the oppositedirection directly follows. In such a situation with current flow in theopposite direction, source of charge carriers 238 and switch 240 wouldbe used to the exclusion of source of charge carriers 228 and switch230.

FIG. 8 shows a partial block diagram, partial electrical schematic, ofan example switch assembly. In particular, the example switch assembly800 comprises a B-TRAN 100 and a driver 802. The B-TRAN 100, in an NPNconfiguration, is shown by way of an example circuit symbol having twoemitters and two bases. The circuit symbol shows the uppercollector-emitter 112, the upper base 114, the lower collector-emitter120, and the lower base 122. The upper collector-emitter 112 is coupledto the upper terminal 224 of the switch assembly 800. The lowercollector-emitter 120 is coupled to the lower terminal 234 of the switchassembly 800. The example driver 802 defines an upper-base terminal 808coupled to the upper base 114, an upper-conduction terminal 810 coupledto the upper collector-emitter 112, a lower-base terminal 812 coupled tothe lower base 122, and a lower-conduction terminal 814 coupled to thelower collector-emitter 120.

The example driver 802 further comprises a controller 816, an electricalisolator 818, and an isolation transformer 820. In order to place theB-TRAN 100 in the various conduction and non-conduction modes, theexample driver 802 includes a plurality of electrically-controlledswitches and sources of charge carriers. In particular, the driver 802comprises the switch 226 that has its first lead coupled to the upperterminal 224, a second lead coupled to the upper base 114, and a controlinput coupled to the controller 816. As before, the example switch 226is shown as a single-pole, single-throw switch, but in practice theswitch 226 may be a FET with the control input being a gate of the FET.Thus, when the switch 226 is made conductive by assertion of its controlinput, the upper base 114 is coupled to the upper terminal 224.

The driver 802 further comprises a source of charge carriers 822illustratively shown as a battery. The source of charge carriers 822 hasa negative lead coupled to the upper terminal 224. Anotherelectrically-controlled switch 824 (hereafter just switch 824) has afirst lead coupled to the positive terminal of the source of chargecarriers 822, a second lead coupled to the upper base 114, and a controlinput coupled to the controller 816. The example switch 824 is alsoshown as a single-pole, single-throw switch, but in practice the switch824 may be a FET with the control input being the gate of the FET. Thus,when the switch 824 is conductive, the source of charge carriers 822 iscoupled between the upper terminal 224 and the upper base 114. Thedriver 802 further comprises another source of charge carriers 826illustratively shown as a battery. The source of charge carriers 826 hasa negative lead coupled to the upper terminal 224. Anotherelectrically-controlled switch 828 (hereafter just switch 828) has afirst lead coupled to the positive terminal of the source of chargecarriers 826, a second lead coupled to the upper base 114, and a controlinput coupled to the controller 816. The example switch 828 is alsoshown as a single-pole, single-throw switch, but in practice the switch828 may be a FET with the control input being the gate of the FET. Thus,when the switch 828 is conductive, the source of charge carriers 826 iscoupled between the upper terminal 224 and the upper base 114. Thesources of charge carriers 822 and 826 may be alone or in combinationthe example source of charge carriers 228 of FIG. 2 .

The driver 802 further comprises the upper-main switch 222 that has afirst lead coupled to the upper terminal 224, a second lead defining theupper-conduction terminal 810 coupled to the upper collector-emitter112, and a control input coupled to the controller 816. As before, theexample upper-main switch 222 is shown as a single-pole, single-throwswitch, but in practice the upper-main switch 222 may be a FET with thecontrol input being a gate of the FET. Thus, when the upper-main switch222 is made conductive, such as by assertion of its control input, theupper terminal 224 is coupled to the upper collector-emitter 112.

Turning now to lower side of the B-TRAN 100, the example driver 802further comprises the switch 236 that has a first lead coupled to thelower terminal 234, a second lead coupled to the lower base 122, and acontrol input coupled to the controller 816. The example switch 236 isshown as a single-pole, single-throw switch, but in practice the switch236 may be a FET with the control input being a gate of the FET. Thus,when the switch 236 is made conductive by assertion of its controlinput, the lower base 122 is coupled to the lower terminal 234.

The driver 802 further comprises a source of charge carriers 830illustratively shown as a battery. The source of charge carriers 830 hasa negative lead coupled to the lower terminal 234. Anotherelectrically-controlled switch 832 (hereafter just switch 832) has afirst lead coupled to the positive terminal of the source of chargecarriers 830, a second lead coupled to the lower base 122, and a controlinput coupled to the controller 816. The example switch 832 is shown asa single-pole, single-throw switch, but in practice the switch 832 maybe a FET with the control input being the gate of the FET. Thus, whenthe switch 832 is conductive, the source of charge carriers 830 iscoupled between the lower terminal 234 and the lower base 122. Thedriver 802 further comprises another source of charge carriers 834illustratively shown as a battery. The source of charge carriers 834 hasa negative lead coupled to the lower terminal 234. Anotherelectrically-controlled switch 836 (hereafter just switch 836) has afirst lead coupled to the positive terminal of the source of chargecarriers 834, a second lead coupled to the lower base 122, and a controlinput coupled to the controller 816. The example switch 836 is shown asa single-pole, single-throw switch, but in practice the switch 836 maybe a FET with the control input being the gate of the FET. Thus, whenthe switch 836 is conductive, the source of charge carriers 834 iscoupled between the lower terminal 234 and the lower base 122. Thesources of charge carriers 830 and 834 may be alone or in combinationthe example source of charge carriers 238 of FIG. 2 .

The driver 802 further comprises the lower-main switch 232 that has afirst lead coupled to the lower terminal 234, a second lead defining thelower-conduction terminal 814 coupled to the lower collector-emitter120, and a control input coupled to the controller 816. As before, theexample lower-main switch 232 is shown as a single-pole, single-throwswitch, but in practice the lower-main switch 232 may be a FET with thecontrol input being a gate of the FET. Thus, when the lower-main switch232 is conductive, such as by assertion of its control input, the lowerterminal 234 is coupled to the lower collector-emitter 120.

The controller 816 defines control inputs 838 and 840, and controloutputs 842, 844, 846, 848, 850, 852, and 854 coupled to the controlinputs of the switches 222, 828, 824, 226, 236, 832, 836, and 232,respectively. When the control input 838 is asserted, the controller 816is designed and constructed to arrange the B-TRAN 100 for conductionfrom the upper terminal 224 to the lower terminal 234 (e.g., FIG. 4 or 5). Oppositely, when the control input 838 is de-asserted, the controller816 is designed and constructed to arrange the B-TRAN 100 to blockcurrent flow from the upper terminal 224 to the lower terminal 234(e.g., the off mode of FIG. 3 ). Similarly, when the control input 840is asserted, the controller 816 is designed and constructed to arrangethe B-TRAN 100 for conduction from the lower terminal 234 to the upperterminal 224. And oppositely, when the control input 840 is de-asserted,the controller 816 is designed and constructed to arrange the B-TRAN 100to block current flow from the lower terminal 234 to the upper terminal224. When the control inputs 838 and 840 are both asserted, thecontroller 816 arranges the B-TRAN 100 for current flow in bothdirections (e.g., AC breaker service), and when the control inputs 838and 840 are both de-asserted, the controller 816 blocks current flow inboth directions.

In some cases the arrangement of the B-TRAN 100 to be in non-conductiveis dependent upon the polarity of the applied voltage. Thus, the examplecontroller 816 may further define a polarity input 856 that receives aBoolean indication of the applied polarity. In the example driver 802, acomparator 858 has a first input coupled to the upper terminal 224 (theconnection shown by bubble “A”) and a second input coupled to the lowerterminal 234. The comparator 858 defines a compare output coupled to thepolarity input 856. While FIG. 8 shows the first and second inputscoupled directly to the respective conduction terminals, in practice thevoltage across the B-TRAN 100 when non-conductive may be large (e.g.,1200V) and thus each of the first and second inputs may be coupled totheir respective conduction terminals by way of respective voltagedivider circuits. In yet still further cases, the applied polarity maybe determined by systems and devices external to the switch assembly800, and a Boolean signal sent across the electrical isolator 818 to thecontrol input 856.

Transitioning the B-TRAN 100 from being non-conductive, to conductive,and then back to non-conductive may be a multistep process. To implementthe multistep process, the controller 816 may be individual circuitcomponents, an application specific integrated circuit (ASIC), amicrocontroller with controlling software, a reduced-instruction-setcomputing (RISC), a digital signal processor (DSP), a processor withcontrolling software, a programmable logic device (PLD), or a fieldprogrammable gate array (FPGA), and/or combinations, configured to readthe control inputs 838 and 840, read the polarity input 856, and drivecontrol outputs to implement the mode transitions of the B-TRAN 100.

In example systems, the switch assembly 800 is electrically floated. Inorder to receive the control inputs 838 and 840 in the electrical domainof the switch assembly 800, the example driver 802 implements theelectrical isolator 818. The example electrical isolator 818 may takeany suitable form, such as optocouplers or capacitive isolation devices.Regardless of the precise nature of the electrical isolator 818,external control signals (e.g., Boolean signals) may be coupled tocontrol inputs 860 and 862 of the electrical isolator 818. Theelectrical isolator 818, in turn, passes the control signals through tothe electrical domain of the switch assembly 800. In the example, theexternal control signals are passed through to become the control input838 and 840 of the controller 816.

Turning now to the isolation transformer 820. Various devices within theswitch assembly 800 may use operational power. For example, thecontroller 816 may use a bus voltage and power to enable implementationof the various modes of operation of the B-TRAN. Further, the sources ofcharge carriers within system may in practice be implemented asindividual voltage sources in the form of switching power converters, orindividual current sources also implemented using switching powerconverters. The switching power converters implementing the sources ofcharge carriers may use bus voltage and power. In order to provideoperational power within the electrical domain of the switch assembly800, the isolation transformer 820 is provided. External systems (notspecifically shown) may provide an alternating current (AC) signalacross the primary leads 864 and 866 of the isolation transformer 820(e.g., 15V AC). The isolation transformer 820 creates an AC voltage onthe secondary leads 868 and 870. The AC voltage on the secondary of theisolation transformer 820 may be provided to an AC-DC power converter872, which rectifies the AC voltage and provides power by way of busvoltage VBUS (e.g., 3.3V, 5V, 12V) with respect to a common 874. Thepower provided by the AC-DC power converter 872 may be used by thevarious components of the switch assembly 800. In other cases, multipleisolation transformers may be present (e.g., one for each side of theB-TRAN). Further still, a single isolation transformer with multiplesecondary windings may be used. The discussion now turns to examplearrangements for making the B-TRAN 100 conductive and/or non-conductivein the context of the switch assembly 800.

Consider, as an example, a situation in which the applied voltage hasthe positive polarity on the upper terminal 224. Further consider thatthe control input 860 applied to the electrical isolator 818 isde-asserted, and thus a control signal applied to the control input 838of the controller 816 is de-asserted. Based on the de-asserted state ofthe control input 838, the controller 816 is designed and constructed toplace the B-TRAN 100 in the off mode taking into account the appliedpolarity (e.g., as read by the controller 816 through the polarity input856). Thus, in the example arrangement the upper-main switch 222 isconductive and the switch 236 is conductive. In some examples switches222 and 236 are made conductive by the controller 816 asserting thecontrol outputs 842 and 850, respectively. However, in other cases, andas described in greater detail below, the switches 222 and 236 areimplemented as FETs with internal body diodes. Thus, the conductivity ofupper-main switch 222 may be based, initially at least, on the appliedvoltage forward biasing the body diode of the FET implementing theupper-main switch 222. Similarly, the conductivity of switch 236 may bebased, initially at least, on the applied voltage forward biasing thebody diode of the FET implementing the switch 236. It follows thecontroller 816 need not necessarily take affirmative action to achievethe current blocking for the assumed polarity of the voltage applied. Asimilar arrangement and/or operation may exist for the lower-main switch232 and the switch 226 when arranged for blocking current for theopposite polarity.

Still considering the example arrangement of the positive polarity atthe upper terminal 224, now consider that the control signal applied tothe control input 860 of the electrical isolator 818 is asserted, andthus the control signal applied to the control input 838 of thecontroller 816 is asserted. Based on the assertion, in the exampleswitch assembly 800 the controller 816 may be designed and constructedto first place the B-TRAN 100 into the optional diode-on mode byasserting the control output 842 (making the upper-main switch 222conductive), asserting the control output 854 (making the lower-mainswitch 232 conductive), de-asserting the control output 850 (making theswitch 236 non-conductive), and asserting control output 848 (making theswitch 226 conductive). Making the switch 226 conductive couples theupper terminal 224 to the upper base 114. The arrangement results in acurrent flow through the B-TRAN 100 and forward voltage dropcommensurate the diode-on mode. When used, the diode-on mode may last apredetermined period (e.g., from about 0.1 μs to 5 μs). The controller816 may be designed and constructed to then place the B-TRAN into thetransistor-on mode by injecting charge carriers into the upper base 114.In the transition from the diode-on mode to transistor-on mode, thecontroller 816 may be designed and constructed to de-assert the controloutput 848 (making the switch 226 non-conductive) and after a sufficientamount of time to ensure the switch 226 is non-conductive, assert thecontrol output 846 (making switch 824 conductive). In the absence ofimplementing the diode-on mode (i.e., from the off mode of FIG. 3 ), thecontroller 816 may be designed and constructed to assert the controloutput 842 (making the upper-main switch 222 conductive), assert thecontrol output 854 (making the lower-main switch 232 conductive),de-assert the control output 850 (making switch 236 non-conductive), andassert the control output 846 (making switch 824 conductive).Regardless, making switch 824 conductive couples the source of chargecarriers 822 between the upper collector-emitter 112 and the upper base114. In some example systems, the source of charge carriers 822 createsa controlled voltage applied across the upper collector-emitter 112 andthe upper base 114 of about 1.0V, which results in current flow into theupper base 114. In the arrangement the injecting of charge carriers intothe upper base 114 increases the number of charge carriers in the driftregion of the B-TRAN 100, which drives the B-TRAN 100 into a saturatedstate.

The second source of charge carriers 826 and related switch 828 may beused to perform different functions in different switch assemblies 800.For example, the voltage produced by the source of charge carriers 826may be higher than the voltage produced by the source of charge carriers822, and thus to decrease switching time from non-conductive to fullyconductive, the source of charge carriers 826 may be coupled to theupper base 114 for a predetermined period of time, and thereafter theinjection of charge carriers may transition to the source of chargecarriers 822 for reasons of increasing overall efficiency (e.g., takinginto account energy used by the switch assembly 800).

In yet still other cases, the voltage produced by the source of chargecarriers 826 may be lower than the voltage produced by the source ofcharge carriers 822, and in order to reduce switching losses associatedwith moving from conductive to non-conductive, a predetermined timebefore the next transition the example switch assembly 800 maytransition to injection of charge carriers using the source of chargecarriers 826 which may increase the forward voltage drop across theB-TRAN 100 but which may decrease switching losses at the nexttransition.

The example operation discussed with respect to FIG. 8 was for theexample applied voltage with the positive polarity on the upper terminal224. Again, however, the example B-TRAN 100 is a symmetrical device, andnow understanding how to arrange the B-TRAN 100 into the variousconductive and non-conductive states, control of current flow in theopposite direction directly follows.

The switch assembly 800 of FIG. 8 utilizes separate and independentsources of charge carriers associated with each side for the twoinjection modes for charge carriers. For example, the upper sideillustratively uses the source of charge carriers 822 and source ofcharge carriers 826, and the lower side illustratively uses the sourceof charge carriers 830 and 834. However, in other cases each side of theB-TRAN 100 may use a single yet variable source of charge carriers, oneeach on each side, to drive inject carriers.

FIG. 9 shows a partial electrical schematic of an example switchassembly. In particular, FIG. 9 shows the example B-TRAN 100 as well asportions of an example driver 802. The driver 802 may likewise have theisolation transformer, the AC-DC power converter, the electricalisolator, the controller, and the comparator, but those components areomitted from the shorthand notation of FIG. 9 . For purposes ofdiscussion, for the upper side 102, FIG. 9 shows the switches 222, 824,226, and 828, as well as the example sources of charge carriers 822 and826. For the lower side 104, FIG. 9 shows the switches 232, 832, 236,and 836, as well as the example sources of charge carriers 830 and 834.

As alluded to above, many of the switches are implemented as FETs. Inthe example switch assembly of FIG. 9 the upper-main switch 222 is shownas a FET having a source coupled to the upper terminal 224, a draincoupled to the upper collector-emitter 112, a gate defining the controlinput, and a body diode coupled between the source and the drain. Whenthe applied voltage has a positive polarity on the upper terminal 224,the body diode is forward biased and thus makes the upper-main switch222 conductive (without action by the controller 816 (FIG. 8 )). Duringconductive states of the B-TRAN 100, and regardless of applied polarity,the controller 816 drives the gate to make the FET conductive to lowerthe overall voltage drop. In example cases, the FET used to implementthe upper-main switch 222 may have a breakdown voltage of 100V or less,and in some cases about 80V, in spite of the fact the B-TRAN 100 mayhave a breakdown voltage of 600V or more, and in some cases about 1200V.

The example switch 226 is shown as pair of back-to-back FETs. Inparticular, the switch 226 is shown as a first FET having a sourcecoupled to the upper terminal 224, a second FET having a source coupledto the upper base 114, and the drains of the FETs are coupled together.The gates of the FETs may be coupled individually to the controller 816(FIG. 8 ), or the gates may be coupled together and driven by thecontroller 816 as a single unit. The FETs each have body diodes, and inthe arrangement shown the cathodes of the body diodes are coupledtogether. Having back-to-back FETs enables bi-directional currentblocking in spite of the presence of the body diodes, as well asbi-directional current flow. For example, the switch 226 may beconductive during the optional diode-on mode (FIG. 4 ) in which, forpositive polarity at the upper terminal 224, current may flow from theupper terminal 224 to the upper base 114 through the switch 226. Duringtransistor-on mode, however, the switch 226 may need to benon-conductive (e.g., to enable other devices to inject chargecarriers). Thus, for positive polarity on the upper terminal 224, whenthe gates are de-asserted the back-to-back FETs block current flow inspite of the body diode of the first FET being forward biased. Insituations in which the positive polarity is at the lower terminal 234,the switch 226 may also be conductive in transitions to and during thetransistor-off mode. For example, the shutoff current in the transitionto the transistor-off mode may be carried by switch 226, along with anyleakage current in the transistor-off mode.

Similarly, switch 824 is shown as a pair of back-to-back FETs. Inparticular, the switch 824 is shown as a FET 900 having a source coupledto the source of charge carriers 822, a FET 902 having a source coupledto the upper base 114, and the drains of the FETs 900 and 902 arecoupled together. The gates of the FETs 900 and 902 may be coupledindividually to the controller 816 (FIG. 8 ), or the gates may becoupled together and driven by the controller 816 as a single unit. TheFETs 900 and 902 each have a body diode, and in the arrangement shownthe cathodes of the body diodes are coupled together. Havingback-to-back FETs enables bi-directional current blocking in spite ofthe presence of the body diodes, as well as bi-directional current flow.With positive polarity on the upper terminal 224, the transistor-on modemay be implemented with the source of charge carriers 822 injectingcharge carriers into the upper base 114 through the FETs 900 and 902. Inother modes, the current flow from the source of charge carriers 822 tothe upper base 114 may be blocked by the FET 902 in spite of the factthe body diode of the FET 900 may be forward biased by the source ofcharge carriers 822.

In example cases, the resistors 904 and 906 enable the switch 824 toserve the functions of both the switch 226 and switch 230 (FIG. 2 ).That is, when the source of charge carriers 822 is used to inject chargecarriers into the upper base 114, the switch 824 serves the function ofswitch 230. However, the FET 902 of the example switch 824, along withthe resistors 904 and 906, also enable the switch 824 to serve thefunction of switch 226. For example, when the positive polarity is onthe lower terminal 234 and the upper-main switch 222 is non-conductive,the shutoff current may flow through the body diode of the FET 902,through the resistor 904 in parallel with the FET 900, and through theresistor 906 in parallel the source of charge carriers 922. Whileeventually the controller 816 (FIG. 8 ) may make switch 226 conductive,the timing constraints are more forgiving because in the examplesituation the body diode of the FET 902 conducts contemporaneously withthe commutation that creates the shutoff current.

Still considering switch 824 and resistors 904 and 906 (and thecorresponding resistors 908 and 910 associated with switch 832 on thelower side 104), the body diodes may be used to enable a power-up safemode. That is, the resistors 904 and 906 ensure race conditions at powerup of the switch assembly 800 do not cause inadvertent conductionthrough the B-TRAN 100. In particular, the switch assembly 800 may havethe upper terminal 224 and lower terminal 234 coupled within an overallsystem. Voltage may appear across the upper terminal 224 and lowerterminal 234, in either polarity, before the AC-DC power converter 872(FIG. 8 ) has powered up, and/or before the controller 816 has had anopportunity to bootstrap to an operational state. Consider, as anexample, a power up condition in which the positive polarity appears atthe upper terminal 224 before the controller 816 is operational. In sucha situation, the body diode of the FET implementing the upper-mainswitch 222 is conductive. Moreover, the body diode of the FET 912 of theswitch 832 will be forward biased, causing the shutoff current and/orleakage current to flow from the lower base 122 to the lower terminal234. A similar arrangement occurs when the positively polarity appearson the lower terminal 234. Thus, even in the absence of control by thecontroller 816, the B-TRAN 100 enters a non-conductive safe moderegardless of the polarity of the voltage applied across the upperterminal 224 and lower terminal 234.

Switch 828 is shown as a single FET having a source coupled to the upperbase 114, a drain coupled to the positive lead of the source of chargecarriers 826, a gate defining the control input, and a body diodecoupled between the source and the drain. As noted above, the source ofcharge carriers 826 may be used for a predetermined period of time whentransitioning the B-TRAN 100 to conductive. The voltage associated withthe source of charge carriers 826 may keep the body diode of the FETreversed biased when the FET itself is non-conductive, and thusback-to-back FETs may not be needed with the respect to the switch 828.

FIG. 9 further shows the lower-main switch 232 as a FET having a sourcecoupled to the lower terminal 234, a drain coupled to the lowercollector-emitter 120, a gate defining the control input, and a bodydiode coupled between the source and the drain. When the applied voltagehas the positive polarity on the lower terminal 234, the body diode isforward biased and thus makes the lower-main switch 232 conductive(without action by the controller 816 (FIG. 8 )). During conductivestates of the B-TRAN 100, and regardless of applied polarity, thecontroller 816 drives the gate to make the FET conductive to lower theoverall voltage drop. In example cases, the FET used to implement thelower-main switch 232 may have a breakdown voltage of 100V or less, andin some cases about 80V, in spite of the fact the B-TRAN 100 may have abreakdown voltage of 600V or more, and in some cases about 1200V.

In similar fashion to switch 226, switch 236 may be implemented asback-to-back FETs. Further, in similar fashion switch 832 may beimplemented as back-to-back FETs. The description of operation ofswitches 236 and 832 are duplicative of the descriptions of switches 226and 824, taking into account the polarity of the applied voltage, andwill not be repeated again here so as not to unduly lengthen thedescription. Similarly, the source of charge carriers 834 may beassociated with switch 836 illustratively shown as a single FET for thesame reasons as discussed with respect to switch 828.

When the various switches are implemented as FETs with body diodes asshown in FIG. 9 , state transitions may be more easily and quicklyimplemented by the controller 816 (FIG. 8 ). Consider, as an example,that the positive polarity is on the upper terminal 224 and that driver802 has the B-TRAN 100 arranged for transistor-on mode. In such asituation, the upper-main switch 222 is conductive, the switch 824 isconductive, the lower-main switch 232 is conductive, and the remainingswitches are non-conductive. Now consider that driver 802 receives acommand to make the B-TRAN 100 non-conductive (e.g., de-assertion ofcontrol input 838 (FIG. 8 )). When the switches are implemented as FETsas shown, arranging the driver 802 to implement transistor-off mode mayinvolve having the controller 816 (FIG. 8 ) de-assert all the gates ofall the FETs. Upper-main switch 222 will remain conductive based on thebody diode being forward biased and conductive. The lower-main switch232 interrupts the current flow and its body diode is reverse biased.While the lower-main switch 232 is used to interrupt the current flow(e.g., 100A), the lower-main switch 232 is not the primary deviceblocking the higher voltage—the B-TRAN 100 performs that task. Thus, thelower-main switch 232 having a breakdown voltage of 100V or less, and insome cases about 80V, is sufficient. The interruption of the currentflow commutates the shutoff current to flow through the body diode ofFET 912 of switch 832 and resistors 908 and 910. At some point in theexample situation, the controller 816 may make switch 236 conductive toreduce current through the resistors 908 and 910, but such is notstrictly required.

Consider again a transition from transistor-on mode to off mode, againin the example situation of the positive polarity at the upper terminal224. When the controller 816 (FIG. 8 ) transitions the B-TRAN 100 fromconductive to non-conductive, the example system of FIG. 9 may extractcharge carriers through the upper base 114 by way of the switchillustratively shown as FET 914 and source of charge carriers 916. Inparticular, when the controller 816 transitions from the transistor-onmode to the off mode, the controller 816 may be designed and constructedto implement an intermediate step by assertion of the gate of FET 914,making the FET conductive and thus coupling the source of chargecarriers 916 between the upper base 114 and the upper terminal 224. Thepolarity of the source of charge carriers 916 extracts charge carriersfrom the drift region through upper base 114, which enables a fastertransition to non-conductive than, for example, implementing thepre-turn-off mode (FIG. 7 ) or electrically floating the upper base 114.Stated in terms of slope of the forward voltage drop, the examplepolarity of the source of charge carriers 916 increases the upward slopeof the forward voltage drop, which decreases switching time and thusdecreases switching losses. In example cases, the source of chargecarriers 916 may be a voltage source (e.g., between 5.0V and 15V,inclusive, illustratively shown as 12V), and extracting the chargecarriers may reduce the time to transition from a conductive state tothe off mode by between about 0.5 μs and 2 μs, inclusive. The diode 918ensures blocking of reverse current flow to the upper base 114 throughthis path of the driver 802. A similar decrease in transition time maybe achieved for situations in which the positive polarity is on thelower terminal 234 by way of FET 920, source of charge carriers 922, anddiode 924.

In yet still other cases, during a transition from transistor-on mode tooff mode, both FET 914 and FET 920 may be made conductive, and thus bothsources of charge carriers 916 and 922 extract charge carriers. Theperiod within which both FETs 914 and 920 are conductive may be arelatively short period, between about 0.5 μs and 2 μs, inclusive.Further still, only one of FETs 914 and 920 may be made conductive aspart of the transition, independent of the polarity applied across theterminals 224 and 234.

FIG. 10 shows a method in accordance with at least some embodiments. Inparticular, the method starts (block 1000) and comprises: conducting afirst load current from an upper terminal of the power module to anupper collector-emitter of the transistor, through the transistor, andfrom a lower collector-emitter to a lower terminal of the power module(block 1002); and then responsive assertion of a first interrupt signal,interrupting the first load current from the lower collector-emitter tothe lower terminal by opening a lower-main FET and thereby commutating afirst shutoff current through a lower base of the transistor to thelower terminal (block 1004); and blocking current from the upperterminal to the lower terminal by way of the transistor (block 1006).The example may further comprise: conducting a second load current fromthe lower terminal of the power module to the lower collector-emitter,through the transistor, and from the upper collector-emitter to theupper terminal (block 1008); and then responsive assertion of a secondinterrupt signal, interrupting the second load current from the uppercollector-emitter to the upper terminal by opening an upper-main FET andthereby commutating a second shutoff current through the upper base tothe upper terminal (block 1010); and blocking current from the lowerterminal to the upper terminal by way of the transistor (block 1012).Thereafter, the method ends (block 1014).

FIG. 11 shows a plot of transient times for transitioning a B-TRAN fromconductive to non-conductive. In particular, FIG. 11 co-plots severalimplementations of diode turn-off of the examples herein, along withcorresponding examples of three-term inal or transistor turn-off of therelated art. The vertical axis is load current through the B-TRAN inAmps, and the horizontal axis is transient time in microseconds from anarbitrary start time. The various plots were created using a simulationprogram (e.g., a Technology Computer-Aided Design (TCAD) program) withthe switch assembly controller current to a resistive load. The exampleplot 1100 shows the transient time for a diode turn-off without theusing a pre-turn-off mode, such as transitioning from transistor-on mode(FIG. 5 ) directly to off mode (FIG. 3 ). Moreover, for the plot 1100the transition begins at an arbitrary time 30 μs, and thus the transienttime from the example 100A of current to effectively zero current occursin about 3 μs (i.e., between the 30 μs point and the 33 μs point). Bycontrast, plot 1102 shows the transient time for a transistor turn-offof the related art without using a pre-turn-off mode, such astransitioning from a conductive mode to a non-conductive mode (FIG. 6 ).As before, for the plot 1102 the transition begins at the arbitrary time30 μs, and thus the transient time from the example 100A of current toeffectively zero current occurs in about 6 μs—twice as long as theexample cases herein.

The transient time for the diode turn-off shown by plot 1100 again iswithout any pre-turn-off. However, the transient time may be made evenshorter by implementation of a pre-turn-off mode (e.g., FIG. 7 ) betweenthe transistor-on mode (e.g., FIG. 5 ) and the off mode (e.g., FIG. 3 ).For example, plot 1104 shows a transient time for a diode turn-off usinga pre-turn-off mode of 5 μs. That is, in example systems the switchassembly may transition from the transistor-on mode (FIG. 5 ) to thepre-turn-off mode (FIG. 7 ) for about 5 μs before transitioning to theoff mode (FIG. 3 ). That is, from the transistor-on mode (FIG. 5 ) theswitch assembly implements the pre-turn-off mode (FIG. 7 ) at about the25 μs point in the horizontal time scale of FIG. 11 . As noted above,the pre-turn-off mode may drain charge carriers from the drift region ofthe B-TRAN, and thus decrease the saturation state of the device, thoughas shown the amount of current through the B-TRAN is reduced onlyslightly. At about the 30 μs point, the example switch assemblytransitions to the off mode (FIG. 3 ), and plot 1104 shows the transienttime associated with the transition. Thus, using the pre-turn-off mode(FIG. 7 ) may make the transient time (measured from the implementationof the off mode of FIG. 3 ) to less than 1 μs. By contrast, as shown byplot 1106, even implementing a pre-turn-off having a duration of 5 μsthe transistor turn-off may be shortened only to just under 3 μs.

Having shorter transient times may have several advantages, not all ofwhich need be present in each implementation. For example, with shortertransient of the diode turn-off, switching losses may be reducedcompared to transistor turn-offs. Comparing switching losses for a diodeturn-off (with no pre-turn-off) to a transistor turn-off (with nopre-turn-off), the switching losses maybe cut in half. Shorter transienttimes also enable higher frequency operation for situations in whichincreased frequency is desired.

While the upper-main switch and lower-main switch each have acorresponding voltage drop when fully conductive, when implemented aspower FETs the forward voltage drops are small (e.g., 0.01V to 0.1 V),and in many cases negligible, compared to the forward voltage drop ofthe associated B-TRAN (e.g., 0.2V to 0.6V). Moreover, it is noted thatthe shutoff current that flows through the base on the opposite sidefrom the positive polarity during a transition from conductive tonon-conductive may have a peak current about equal to the load current;however, while the base regions and connections may not be designed tohandle full load current for extended periods of time, the inventors ofthe present specification have found through simulations that given thetransient nature of the shutoff current (e.g., 1 μs to 3 μs), evenshutoff currents with peaks equal to the load current do not adverselyaffect operation of the device.

Many of the electrical connections in the drawings are shown as directcouplings having no intervening devices, but not expressly stated assuch in the description above. Nevertheless, this paragraph shall serveas antecedent basis in the claims for referencing any electricalconnection as “directly coupled” for electrical connections shown in thedrawing with no intervening device(s). Moreover, this paragraph shallnot negate that a base electrically connected to a collector-emitterthrough a transistor may be referred to as “directly coupled.”

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A method of operating a power module havingbi-directional double-base bipolar junction transistor, the methodcomprising: conducting a first load current from an upper terminal ofthe power module to an upper collector-emitter of the transistor,through the transistor, and from a lower collector-emitter to a lowerterminal of the power module; and then responsive assertion of a firstinterrupt signal interrupting the first load current from the lowercollector-emitter to the lower terminal by opening a lower-main FET andthereby commutating a first shutoff current through a lower base of thetransistor to the lower terminal; and blocking current from the upperterminal to the lower terminal by the transistor.
 2. The method of claim1: wherein interrupting the first load current further comprisesinterrupting the first load current with the lower-main FET having abreakdown voltage of 100 Volts or less; and wherein blocking currentfurther comprises blocking at an applied voltage across the upperterminal and the lower terminal of 600 Volts or greater.
 3. The methodof claim 1 further comprising, after blocking current from the upperterminal to the lower terminal: conducting a second load current fromthe lower terminal of the power module to the lower collector-emitter,through the transistor, and from the upper collector-emitter to theupper terminal; and then responsive to assertion of a second interruptsignal interrupting the second load current from the uppercollector-emitter to the upper terminal by opening an upper-main FET andthereby commutating a second shutoff current through an upper base tothe upper terminal; and blocking current from the lower terminal to theupper terminal by the transistor.
 4. The method of claim 3: whereininterrupting the second load current further comprises interrupting thesecond load current with the upper-main FET having a breakdown voltageof 100 Volts or less; and wherein blocking current from the lowerterminal to the upper terminal further comprises blocking at an appliedvoltage across the lower terminal and the upper terminal of 600 Volts orgreater.
 5. A switch assembly comprising: an upper terminal, a lowerterminal, and an upper-control input; a transistor defining an upperbase, an upper collector-emitter, a lower base, and a lowercollector-emitter; an upper-main FET defining a first lead coupled tothe upper terminal, a second lead coupled to the uppercollector-emitter, and a gate; a lower-main FET defining a first leadcoupled to the lower collector-emitter, a second lead coupled to thelower terminal, and a gate; a controller coupled to the upper-controlinput, the gate of the upper-main FET and the gate of the lower-mainFET, and for a first applied voltage across the upper terminal and lowerterminal, the controller configured to: assert the gate of theupper-main FET to make the upper-main FET conductive, arrange thetransistor for conduction from the upper collector-emitter to the lowercollector-emitter, and assert the gate of the lower-main FET to make thelower-main FET conductive such that a first load current flows from theupper terminal to the lower terminal; sense de-assertion of theupper-control input; and responsive to de-assertion of the upper-controlinput de-assert the gate of the lower-main FET to interrupt the firstload current and thereby commutate a first shutoff current through thelower base to the lower terminal; and arrange the transistor to blockcurrent flow from the upper terminal to the lower terminal.
 6. Theswitch assembly of claim 5 wherein the breakdown voltage of thetransistor is 600 Volts or greater, and the breakdown voltage of thelower-main FET is 100 Volts or less.
 7. The switch assembly of claim 5wherein the breakdown voltage of the transistor is about 1200 Volts, andthe breakdown voltage of the lower-main FET is 80 Volts or less.
 8. Theswitch assembly of claim 5 further comprising: an upper-base FET havinga first lead coupled to the upper base, a second lead coupled to theupper terminal, and a gate, and during periods when the first loadcurrent flows from the upper terminal to the lower terminal, theupper-base FET is conductive; and wherein when the controller arrangesthe transistor to block current flow from the upper terminal to thelower terminal, the controller is further configured to de-assert thegate of the upper-base FET to electrically float the upper base.
 9. Theswitch assembly of claim 5 further comprising: a lower-control inputcoupled to the controller; and wherein for a second applied voltageacross the upper terminal and lower terminal, the second applied voltagehaving a polarity opposite the first applied voltage, the controller isfurther configured to: assert the gate of the lower-main FET to make thelower-main FET conductive, arrange the transistor for conduction fromthe lower collector-emitter to the upper collector-emitter, and assertthe gate of the upper-main FET to make the upper-main FET conductivesuch that a second load current flows from the lower terminal to theupper terminal; sense de-assertion of the lower-control input; andresponsive to de-assertion of the lower-control input de-assert the gateof the upper-main FET to interrupt the second load current and therebycommutate a second shutoff current through the upper base to the upperterminal; and arrange the transistor to block current flow from thelower terminal to the upper terminal.
 10. The switch assembly of claim 9further comprising: a lower-base FET having a first lead coupled to thelower base, a second lead coupled to the lower terminal, and a gate, andduring periods when the second load current flows from the upperterminal to the lower terminal, the lower-base FET is conductive; andwherein when the controller arranges the transistor to block currentflow from the lower collector-emitter to the upper collector-emitter,the controller is further configured to de-assert the gate of thelower-base FET to electrically float the lower base.
 11. The switchassembly of claim 9 wherein the breakdown voltage of the transistor is600 Volts or greater, and the breakdown voltage of the lower-main FET is100 Volts or less.
 12. A method of operating a bi-directionaldouble-base bipolar junction transistor, the method comprising: makingthe transistor conductive from an upper collector-emitter to a lowercollector-emitter by supplying current to an upper base of thetransistor and electrically floating a lower base of the transistor; andthen making the transistor non-conductive by electrically floating theupper base, electrically floating the lower collector-emitter, andconducting a shutoff current through the lower base of the transistor.13. The method of claim 12 wherein electrically floating the lowercollector-emitter further comprises making non-conductive a lower-mainelectrically-controlled switch having a first lead coupled to the lowercollector-emitter.
 14. The method of claim 12 wherein making thetransistor conductive further comprises: closing an upper-mainelectrically-controlled switch coupled between an upper terminal and theupper collector-emitter; and closing a lower-mainelectrically-controlled switch coupled between a lower conductorterminal and the lower collector-emitter.
 15. The method of claim 14wherein making the transistor non-conductive further comprises: openingthe upper-main electrically-controlled switch; conducting the shutoffcurrent to the upper collector-emitter through a diode associated withthe upper-main electrically-controlled switch; and commutating theshutoff current from the lower collector-emitter to the lower base byopening the lower-main electrically-controlled switch.
 16. The method ofclaim 12 wherein conducting the shutoff current through the lower basefurther comprises conducting current through a diode associated with anelectrically-controlled switch having a first lead coupled to the lowerbase.
 17. The method of claim 12 wherein supplying current to the upperbase further comprises at least one selected from a group comprising:supplying current at a base voltage about the same as a collectorvoltage applied to the upper collector-emitter; and supplying current tothe upper base at the base voltage higher than the collector voltage.